Printing systems that deflect drops using a gas flow are known, see, for example, U.S. Pat. No. 4,068,241 (Yamada). When using a system with multiple printheads, however, it is important that colors for each of the printheads be consistent. This consistency must be both within a run and from run-to-run.
When printing with multiple printheads a number of parameters come into play which affects the darkness or optical density of the print from each printhead. Some of these factors may be the shape and diameter for the nozzle of each printhead, ink pressure, drop creation frequency, printing speed, and the concentration of the ink. Various attempts have been made to solve this problem. For example, U.S. Pat. No. 7,273,272 (Inoue) inserts a device into the flow path for altering resistance to the flow of ink.